Adding whitespace escaping on difference display

[OlegP-andrew]

Solves #10704.

Resolved issue of terminal output showing unhelpful messages if the differentiating symbols are whitespaces.

Solution in util.py/_diff_text:

diffspace = False
for i in range(min(len(left), len(right))):
        if left[i] != right[i]:
            if left[i].isspace() and right[i].isspace():
                diffspace = True  # Check if difference in strings is whitespace symbol
                break
    if left.isspace() or right.isspace():
        left = repr(str(left))
        right = repr(str(right))
        explanation += ["Strings contain only whitespace, escaping them using repr()"]
    elif diffspace:
        left = repr(str(left))
        right = repr(str(right))
        explanation += [
            "Strings are different by whitespaces, escaping them using repr()"
        ]

We go through the compared strings, checking if any differentiating symbols are both whitespaces,
after which, unless the strings are already fully escaped due being just whitespace, we escape them using
repr() adding explanation why that's happening.

Testing:

pytest.param(
        """
        def test_this():
            assert "word\t" == "word    "
        """,
        """
        >       assert "word\t" == "word    "
        E       AssertionError: assert 'word\\t' == 'word    '
        E         Strings are different by whitespaces, escaping them using repr()
        E         - 'word    '
        E         + 'word\\t'
        """,
        id="Compare whitespaces",
    )

Adding new parameter to test_error_diffs which tests the behaviour of displaying whitespaces correctly.
Output of test in the terminal:

[OlegP-andrew]

There's consideration to add escaping if the difference between the two strings is stuff like trailing spaces. Current solution only works if different symbols exist in both strings and are whitespaces, so something like difference by trailing whitespace might still be not humanly
readable in the difference.